The present invention relates to apparatus and methods for milling and, more particularly, to apparatus and methods for milling materials stuck in down-hole operations.
In milling apparatuses- for milling material such as metal stuck in casings or drilled bores in down-hole operations, e.g., in well bores, a mill including a mill face, referred to herein as "mill face" for convenience, is disposed at the bottom end of a shaft and turned to mill the stuck material. As in, for example, earth boring operations, pressurized water may be circulated to the bottom of the mill face to facilitate milling of the material being milled, to keep the temperature of the mill face down, and to carry away the milled particles.
It is often desirable to mill material having a larger diameter than the maximum outside diameter of the mill face able to be provided in the bore or casing. One technique for milling under such circumstances is to offset the centerline of the usually circular mill face from the centerline of the usually circular shaft. In U.S. Pat. Nos. 712,887 to Wyczynski and 4,183,415 to Stenuick, for example, variations on the general theme of drilling holes with offset or eccentric drilling devices are shown.
When the mill face is turned in the material being milled, it is desirable to stabilize the shaft relative to the casing or bore wall to ensure that the mill face contacts the surface being milled at the proper location relative to the centerline of the casing. This is particularly so in offset milling operations where it is generally necessary to use a mill face and a shaft connected to the mill face having smaller outside diameters than the inside diameter of the casing or bore. Known stabilizing assemblies tend to be permanently fixed on an exterior surface of the shaft between the shaft and the inner casing or bore wall. Such stabilizing assemblies can render movement of the mill face and the stabilizing assembly within the casing or bore difficult. Accordingly, it is desirable to provide an offset milling device including a stabilizing assembly that is easy to maneuver in the casing or bore.
In accordance with one aspect of the present invention, a mill assembly for downhole milling in a bore includes a mill face and means for extending the mill face into a bore. Means for stabilizing the extending means in the bore are provided and include a cam and a cam follower in contact with the cam. One of the cam and the cam follower are axially movable so that the cam follower is moved radially outward from a centerline of the stabilizing means.
In accordance with another aspect of the present invention, a mill assembly for downhole milling in a bore includes a mill face and a shaft for extending the mill face into a bore and into contact with a material to be milled. Means, connected at one end to the mill face and having a smaller diameter than the first diameter, are provided for stabilizing the shaft in the bore, and include a stem having one or more tapered surfaces, the tapered surfaces tapering from a first diameter to a second diameter larger than the first diameter, a plurality of roller bearings circumferentially retained in a plane around the stem, each roller bearing being in contact with one of the tapered surfaces at a first point. One of the roller bearings and the stem are axially movable such that each of the plurality of roller bearings contacts the tapered surface at a second point closer to the second diameter than the first point and is thereby moved axially outward from a centerline of the stem.
In accordance with yet another aspect of the present invention, a method of milling a material in a longitudinal opening having an inside diameter defined by an internal wall, with a mill face at the end of a shaft is disclosed. In the method the mill face at the end of the shaft is extended into the longitudinal opening and into contact with the material to be milled. The shaft is stabilized relative to the internal wall of the longitudinal opening by axially moving one of a cam and a cam follower, the cam and the cam follower forming a part of the shaft, relative to one another so that the cam follower is moved radially outward from a centerline of the shaft and toward the internal wall of the longitudinal opening.